1. Field of the Invention
The present invention concerns centrifugally operated variable speed drive pulleys of the kind comprising a hub constrained to rotate with a shaft and, around the former, in face-to-face relationship and adapted to receive a transmission belt, two annular flanges at least one of which, hereinafter referred to as the mobile flange, slides along the hub under the control of a diaphragm spring carrying flyweights. In the conventional manner this diaphragm spring is constituted by a peripheral part forming a Belleville spring, bearing against the mobile flange in such a way that it is able to flex, and a central part divided into fingers bearing on a transverse bearing member mounted on the hub, likewise in such a manner as to be able to flex. Pulleys of this kind are used in particular to drive automobile vehicle ancillary equipments from the motor.
2. Description of the Prior Art
Pulleys of this type are described in particular in French Pat. No. 2 516 622, filed Nov. 18, 1981.
As is well known, a diaphragm spring is a frustoconical annular spring, the cone angle of which varies as a function of the torque exerted on it in diametral axial planes. The presence of flyweights attached to the diaphragm spring is intended to apply to the latter a torque which varies with the rotation speed of the pulley so as consequently to modify the distance between the two annular flanges of the latter by varying the axial loads applied to the mobile flange and thus to the belt. In the conventional manner these flyweights, which are generally massive in form, have their center of gravity as far removed as possible from the diaphragm spring in order to exert on the latter as high a torque as possible for a given flyweight mass.
One effect of this overhang is the creation of very high stresses in the areas where the flyweights are fixed to the diaphragm spring, whence the risk of rupture and thus of an accident arising out of the projection of the flyweights thus detached from the diaphragm spring as if thrown from a sling.